AnswerHello Jen! According to the model number supplied the crisper cover insert part number 5303281398 is the correct replacement part listed for your appliance by the manufacturer and will fit your unit. Thanks!

AnswerHello Sarah! Yes, the insert pan cover 5303281398 is the correct glass cover for the crispers on your Frigidaire model FRT18SJGW1. We do not have the exact measurement, however, judging from our photo it is approx 25" x 12 3/4". Thanks.